OPTICAL-PROPERTIES OF INSULATOR EXCITONIC-SEMICONDUCTOR SUPERLATTICES IN THE PRESENCE OF INERT LAYERS

We study the optical properties of an insulator-excitonic-semiconductor superlattice in the presence of exciton-free inert layers on both surfaces of each semiconducting region. Generalized boundary conditions are applied at the-interface between the inert layer and the active region, and the dispersion relation of the collective normal modes of an infinite superlattice is calculated near an excitonic transition. We also obtain the optical reflectance of a semi-infinite superlattice for p polarization. We present results for CdS layers using two well-known additional boundary conditions. Increasing the inert-layer thickness induces a blueshift and modifies the structure in the complex spectra. This structure is interpreted in terms of guided transverse- and longitudinal-wave resonances in the active excitonic layers.